In recent years, the analog processing of signals has grown in importance, especially with the advent of neural networks and fuzzy logic, and many attempts have been made, with varying degrees of success, at implementing and integrating processors which could carry out such processing.
Among the different problems posed by the making of processors which can perform well and, therefore, be of real commercial value, are the need for the processing to be unaffected by changes in temperature and variations in process parameters, and the programmability of the type of processing as identified by the values of processing coefficients.
The former problem has already been addressed, for example, by M. Sasaki and F. Ueno in an article "A Novel Implementation of Fuzzy Logic Controller Using New Meet Operation", Proceedings of the Third IEEE International Conference on Fuzzy Systems, Jun. 26-29, 1994, pages 1676-1681. The solution proposed there is based on the use of two independent reference signals, namely a current signal and a voltage signal. This is not easy to implement in any reliable manner if high performance is sought; the problem of programmability, moreover, is not addressed, nor is that of how to compensate for variations in the processing coefficients.
The latter problem has already been addressed, for example, by J. W. Fattaruso, S. S. Mahant-Shetti and J. Brock Barton in an article "A Fuzzy Logic Inference Processor", IEEE Journal of Solid-State Circuits, Vol. 29, No. 4, April 1994. This approach involves the use of at least one memory of the RAM type in which several processing coefficients are programmed by a "master" digital processor in digital form, as well as of various digital-to-analog converters. If a processor is to process analog input signals analogically and to output analog signals, storing the coefficients in digital form does not seem to be the natural and more convenient choice.
It is an object of this invention to provide an analog processor which can perform high-quality processings, unaffected by operating temperature and process parameters, in a reliable manner using fairly simple circuitry.